I checked the RPO codes on my '96 and it came with the limited slip rear end. I haven't really noticed this thing working yet, I have punched it a few times and only the right rear lights up.
There are no immediate signs that anyone has had the rear apart but the truck has 155,000 on it. Do these carriers need to be rebuilt? Is it common for them to fail?
Thanks!

 

If the posi unit is like the older posi units, then there are friction surfaces in the rear carrier that could wear out over time. One thing that will kill these faster than anything is the lack of maintanence on the rear end (ie fluid changes). I have always changed all of my diff/t-case fluids every 45-50k miles on every 4x4 vehicle that I have ever owned. Also, you should always use recommended oils. If someone had done a rear end service on your blazer and did not use oil that was formulated for use in limited slip diffs (GL-5), then it is very easy to see why it is not working properly and may never work properly again without replacement of the friction surfaces.

The first thing that I would try would be to drain the rear end, clean it out VERY well with brake parts cleaner, making sure to get any debris out, and fill it back up with a quality rear end oil. I am partial to Mobil products and have used Mobil 1 synthetic 75w90 gl5 in many posi rear ends without any difficulties. The rear in your blazer should contain 1-3/4 qts of fluid so if you buy 2 qts, you should have enough even if you spill some.

 

Great! Thanks for the info.
I'll pick up some oil and brake cleaner at the store tomorrow.

On a side note, will the brake cleaner hide in the axle tubes and thin the oil at all? Will I need a new gasket or will RTV suffice?
Thanks!

 

I didn't spray down close to the axles, just stayed up in the center around the carrier and up in the front of the case. I also let it sit open to air for atleast 15-20 minutes after I wiped out the excess oil/cleaner with a lint free rag. I say lint free, but the best thing to use is the blue paper shop towels, but don't scrub around in there because they will shread on the rough cast inner surface of the diff case. If you air it out well enough, all of the brake cleaner will evaporate and nothing will be left to dilute anything.

Last time I did this job was on my '97 Ram with a limited slip diff. I sprayed down EVERYTHING inside until what was running out the diff (and into a catch can) was almost clear. I just kept moving the spray nozzle around the whole time. You will be able to tell when it's good and clean. I went through 2 cans of brake cleaner during that process. On that diff, I just used a good RTV sealant that was rated for oil. I beleive it was Permatex Ultra Black. Make sure that you thoroughly clean off both the mating surfaces to ensure a leak free seal when done. Both surfaces should be cleaned with brake cleaner once all of the internal cleaning is done and before the sealer is put on. If you have the option to buy a rubber gasket, go with it. The rubber gasket will last through MANY changes, while the RTV is just a pain in the butt to remove when the time comes for another change.

Also, if you have a suction tool to remove the oil through the fill tube, the job will be much cleaner. The other option is to remove all bolts but the top outside 2 (just loosen them) and then pry out on the bottom. You have to be prepared with a rather large pan to make sure that you catch all of the fluid cause it'll come out of there in a rather large rush.

Another thing is that if, when you do the change, you notice a lot of particles in the old oil, you probably are looking at the friction material and it is quite possible that your diff will need reconditioning/replacement.

 

Cool. Thanks for taking the time to help. Looks like a good project for the coming weekend - After the demolition derby at the local rodeo grounds on Saturday 'woo-hoo'!

 

Have fun! I had to miss the demo's here this year because my son is only 12 weeks old (not old enough to be around smoke, loud noises and drunks - me included). Next year should be a blast with him.

No problem on the explaination. If you run into any problems, I should be around all of next weekend. Just post away and I'll get back to here whenever possible. Good luck!

 

Kyle,
Congrats on your son! I have a child due December 28th, not sure of gender yet and I may not get to live my lifes dream of being 'Dad' (too much competition with Mom - lol) but I am going to take my neice, nephew and a teen I know who's father is a deadbeat. They will enjoy the demo for you!!!!

I would take being home with my 12 month old ANYTIME over watching cars fight!!!